A negative polarity plasma focus is operated with the inner electrode as the cathode. So far very little is known of the negative polarity plasma focus except that its neutron yield is considerably lower than that of a normalpositive polarity plasma focus. In order to understand good focusingmechanism a negtive polarity plasma focus has been developed. The device is a 3.3 kJ Mather type with operating pressures of 1 to 10 mbar, energized by a single 15 kV, 30 uF capacitor bank. Electrical characteristics such asvoltage spike and current dip at different operating pressures are examined. In the low pressure regime (1 to 3 mbar) voltage spike and current dipsignal are absent. At 4 mbar deuterium operating pressure a weak voltage spike and current dip is seen in the first half cycle of the signal. For operating pressures greater than 5 to 10 mbar, voltage spike and current dip is observed in the first and second half cycle of the signal. the average axial velocity of the current sheath os - 5.5 cm/us. Results are also compared witha positive polarity focus of a similar type and energy. The dynamical behaviour of the current sheath in the acceleration and radial phasewas also studied using ;aser shodowgraphy technique. For this purpose a TEA nitrogen laser and a nitro-dye laser system have been developed. Comparisons of shodowgraphs are made between a negative and positive polarity focus. The negative polarity focus was found to produce shadowgraphs that are different from a positive polarity focus in the radial phase. There is no difference in the axial phase.